1. Field of the Invention
The invention relates to a method and apparatus for the high temperature annealing of metallic coils and more particularly to a method and apparatus whereby the coil is supported in a horizontal position in the annealing furnace by support means, a portion of which passes through the eye of the coil, said portion being the only part of the support means contacting the coil.
2. Description of the Prior Art
It will be understood by one skilled in the art that the method and apparatus of the present invention may be employed during a high temperature anneal for any purpose and applied to any metallic coiled material. As used herein, the terms "metallic coil" and "metallic coiled material" refer to metallic strip stock wound about a mandrel or the like of a conventional coiling machine, all as is well known in the art. When each coil is removed from the coiling machine mandrel, it comprises a hollow cylindrical element having a plurality of convolutions. For purposes of clarity and convenience, the central, axial hollow of the coil, defined by the convolutions and formed and filled by the coiling machine mandrel during the coiling operation will hereinafter be referred to as the "eye" of the coil.
As used herein, the term "high temperature anneal" refers to an anneal conducted at such a temperature that a coil resting on its end or its side within an annealing furnace would tend to buckle or sag and when standing on end (and in the absence of an adequate annealing separator between the convolution edges at the end upon which it rests) would have its convolution edges upon which it rests stick or weld together. As a consequence, the present invention is directed to anneals of the type generally conducted above about 1100.degree.F. The final high temperature anneals employed in the production of silicon irons having preferred orientations for electrical uses, for example, are frequently conducted at temperatures within the range of from about 1900.degree.F to about 2300.degree.F. The final high temperature anneal employed in the production of cubic texture silicon-iron is an excellent example of an anneal wherein the teachings of the present invention may be advantageously employed. Therefore, the invention will, for purposes of an exemplary showing, be described in terms of its application in such an anneal, although it is to be understood that the invention is not intended to be so limited.
Cubic textured silicon-iron, frequently referred to as cube-on-face oriented silicon-iron, is characterized by high straight-grain and high cross-grain permeabilities and has preponderantly a (100)[ 001] crystal orientation by Miller's indices. Such material is well known in the art and methods for its manufacture are taught in U.S. Pat. Nos. 3,130,092; 3,130,093; 3,130,094 and 3,130,095. In all of these methods, the cubic texture or cube-on-face orientation is achieved during the secondary grain growth stage of the final anneal by virtue of the surface energy phenomenon. The final anneal is conducted at a temperature of from about 1900.degree.F to about 2300.degree.F (and preferably about 2200.degree.F). The annealing atmosphere during the final high temperature anneal may be an inert gas such as argon or helium. Dry hydrogen is a preferred annealing atmosphere. A minute amount of a highly polar compound may or may not be added to the annealing atmosphere or the annealing separator. A non-glass forming annealing separator is used. A preferred annealing separator comprises alumina powder dusted upon the coil convolutions.
In accordance with prior art practice, the final high temperature anneal was generally performed in an annealing furnace in which each of the coils rested upon one of its ends with its axis vertically oriented. Such procedure, however, led to a number of problems. First of all, in this configuration, the coil at high annealing temperatures had no strength and tended to buckle. Of an even more serious nature, however, was the fact that during the dusting of the alumina annealing separator on the coil convolutions, the convolution edges are not coated. As a result of this, the coil convolution edges upon which the coil rested would tend to stick or weld together as a result of the pressure from the weight of the coil and the high temperature. This sticking or welding of the coil convolution edges has constituted a serious problem believed to be largely unavoidable by prior art workers, although much time and effort has been expended on development of improved annealing separators.
U.S. Pat. No. 3,084,081 teaches the laying of coils on their sides for various puposes during at least the initial stages of a final anneal. This patent, however, is not directed to silicon-irons having a cube-on-face orientation and clearly teaches that if the anneal requires temperatures above 1100.degree.F, the coils must be set up on their ends, as is conventional.
The present invention provides a method and apparatus whereby a metallic coil, provided with any appropriate separator including alumina powder applied by dusting, may be subjected to a high temperature anneal for the required period of time without sagging, buckling or sticking or welding of the convolution edges.